As will be apparent from the aforementioned copending application, the use of liquid propellant for barrel-type weapons, i.e. to propel projectiles from the barrels of such weapons, is of significance in many cases in which cartridge-type munitions are unnecessary or disadvantageous.
This is because the liquid propellant can be stored in a convenient way in tanks in the region of the weapon and can be fed also in a simple manner to the combustion chamber of the weapon, e.g. by a metering pump or the like.
Liquid propellants have the advantage that, by controlling the composition of the propellant and/or the quantity thereof fed to the weapon, the muzzle velocity of the projectile can be adjusted at will and hence its firing range can be varied in a particularly simple or convenient manner.
It is known to provide liquid propellants such as hydrazine, isopropyl nitrate, nitromethane and the like for firing barrel weapons with liquid propellants.
In general, the liquid propellants may be so-called monopropellants in which the fuel is premixed with an oxidizer and is ignited by an igniter at the firing chamber of the weapon, or bipropellants in which the oxidizer is combined with the fuel at the chamber. In both cases, for the purposes of the present invention, the fuel or propellant should be nonhypergolic, i.e. not spontaneously ignitable by contact of the oxidizer with the fuel.
Work with liquid propellants such as hydrazine, isopropyl nitrate, nitromethane and the like has shown that the firing pattern is not always reproducible.
The problem appears to arise, with conventional liquid-propellant-fired barrel weapons, from two mechanisms which come into play and interact upon ignition.
The first is the significant dependency of the ignition and propagation of the ignition upon the configuration, extent and nature of the propellant surface. This surface varies during the ignition and combustion operations.
The second significant effect is that of the shock waves which are invariably generated upon ignition and which travel through the liquid propellant and repeatedly are reflected from the combustion chamber walls. As a result of these shock waves, high-pressure peaks can be observed.
Since gas bubbles almost invariably are present in the liquid propellant, these shock waves bring about compression followed by expansion of the bubbles and premature ignition at selected locations with increase in the magnitude and number of these shock waves.
To avoid these disadvantages it has been proposed to provide clusters of passages or elements within the vaporization and/or combustion chamber so as to improve the uniformity of the gasification process (see the aforementioned copending application). Other techniques which have been proposed include the mixing of surface-active agents with the liquid propellant so as to foam the latter and provide an extremely large surface area at which gasification or combustion can occur.
While both of these techniques have been found to be effective to some degree and may be used in conjunction with the present invention, they have by themselves been found to have certain disadvantages. For example, the first technique requires modification of the structure of the weapon to a significant degree. This is not desirable where improvements in the firing of existing weapons without structural modification thereof are desired. The second technique provides an inordinately large volume for the propellant which also may require enlargement or modification of the firing chamber.